Effects of Lattice Relaxation on Composition and Morphology in Strained InxGa1−xAsySb1−y Epitaxial Layers

InxGa1−xAsySb1−y is an important semiconductor material for a variety of mid-infrared devices. Its tunable bandgap, adjustable lattice constant, and other material properties make it appealing for developing optoelectronic devices in the 2 μm to 4 μm region. In this work, we report on the mechanisms of strain relaxation in InxGa1−xAsySb1−y epitaxial layers with low arsenic and high indium concentrations grown on GaSb (100) substrates. Samples were grown via solid-source molecular beam epitaxy with indium mole fractions between x = 0.1 (0.7% lattice mismatch) and x = 0.4 (2.5% lattice mismatch), and arsenic mole fractions between y = 0 and y = 0.02. Sample thicknesses between 10 nm and 100 nm were produced in order to observe the progression of structure formation. Samples were monitored in situ via reflection high-energy electron diffraction and ex situ using scanning electron microscopy, energy-dispersive spectroscopy, Rutherford backscattering spectroscopy, backscattering Raman spectroscopy, and atomic force microscopy. Results suggest that strain relaxation occurs preferentially along the [011] direction, although some crosshatching is observed. A compositional gradient in the growth direction is also observed, suggesting preferential incorporation of gallium at strained interfaces in order to minimize strain energy.